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64 LIGHT AND WATER
obliguely (at an angle of 80"), a much larger portion
(about one-third) escapes at the surface and is re¬
flected along Oe.! Figs. 25 (III) and (IV) are
similar to (1) and (II) respectively, the light now
travelling in the direction of the arrows from a source
below the surface, and here in the same way a much
larger proportion of the beam CO passes out of the
water than of the more oblique beam ¢QO, which is
nearly all reflected down again to a.
Fig. 25 (III). Fig. 25 (IV).
If Figs. 25 (1) and (III) were placed one on the
top of the other, the point O on the point O, and the
line MN on the line MN, then the lines OE, OD,
in each diagram would also coincide. A combination
of the two diagrams would therefore represent the
light coming to the eye, if placed at E and directed
. The following figures are taken from " Light,” by Professor
Tyndall. At perpendicular incidence,
(ze, at 0") water reflects 18 rays per 1,000
: at 40. ,9 99 22 99 9 3?
at 60 )) )) 65 )) 9) ))
at 80 99 99 333 ” ,)
whilst at 891 9 ‘3 721 ,, ) 3